Backstory: You started out on pacifist, refusing to kill, or even do damage. However, you wanted to see what would happen if you killed absolutely no one EXCEPT Sans' brother, Papyrus. So you went through the game, sparing everyone except for Papyrus. But what you didn't expect, is what Sans would do because of this...
@loganvcairns made the attack creator, thanks to him! I made everything else (attacks, dialogue, etc) Fact: Sans increased your LV because he believes only killing the one person you were told not to kill, is pure evil.